=Exp. with Arrowroot.= Make a thin paste by boiling a little arrowroot and water together. When cool test it with a drop of the iodine solution. The characteristic blue color will be very strong, showing that arrowroot is rich in starch. Similar tests may be made with grated potato, wheat-flour, rice-flour, tapioca, and other starch-containing substances. Also powdered sugar, cream of tartar, and other substances may be tested, when it is suspected that they have been adulterated with starch. Although starch grains burst and form a paste with water at 140° Fahr., that is not the temperature at which it should be cooked for food, and the thickening which then takes place should not be confounded, as often happens, with the true cooking of starch. In order to understand the difference between the proper cooking of starch and the simple bursting of the grains, let us consider the changes which take place in starch when it is subjected to different degrees of heat, and also those which are produced in it during the process of digestion. All starch in food is changed into dextrine and then into sugar (glucose, C_{6}H_{12}O_{6}) in the process of digestion. Glucose is a kind of sugar, resembling cane-sugar, but it is not so sweet. =Dextrine.= Dextrine is a substance having the same chemical nature as starch, but differing in many of its properties. It may be described as a condition which starch assumes just before its change into glucose. =Exp. to show Dextrine.= Carefully dry and then heat a little starch to about 400° Fahr. Keep it at this temperature until it turns brown, or for ten minutes. Then mix it with water, when it will dissolve, forming a gummy solution. Starch will not do this. Test it with iodine; it will not change color. The remarkable thing about the relation of dextrine to starch is that although they differ so much in properties they have the same chemical composition.